Earthquake-Resistant Design and Urban Planning

Modern earthquake-resistant engineering rests on the principle that a structure need not remain undamaged in a major earthquake, but must remain standing long enough for occupants to escape, a philosophy known as life-safety design and embodied in the building codes most seismically active countries have adopted since the mid-twentieth century. Base isolation, one of the most effective techniques, physically decouples a building's superstructure from its foundation using flexible bearings, often made of layered rubber and steel or lead-rubber composites, that allow the ground to move rapidly beneath the building while the structure above moves far more slowly, dramatically reducing the forces transmitted to it; the technique has been used in structures ranging from Utah's Salt Lake City and County Building to Japan's post-Kobe generation of hospitals and government buildings, where continued function immediately after an earthquake is considered essential.